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If you are just starting out and in novice or early bronze league, the rewards will get better as you progress after winning more battles. Also, keep a look on the DEC capture rate, if it is below 50%, I recommend that you stop playing for a while and let the capture rate increase. I try to keep it above 75%.

Joining a guild will give you a little bonus to your capture rate. Different types of cards also give a bonus, Alpha edition cards, gold foil cards and promo cards all give a 10% boost to DEC capture rate.